Wash and cook the rice to taste in lightly salted water. Drain and let cool for recipe time.
Rinse the kidneys well in cold water.
In a large saucepan, cover the kidneys with cold water, add 1 tablespoon of white vinegar and bring to a boil. Discard the water and rinse the kidneys in cold water.
Repeat the previous step 5 times, except that the last time no more vinegar is added.
Grate each kidney around the core, avoiding touching the midribs. Set aside.
In a thick, uncovered Presto®-style pot, preheat the oil and blanch the chopped onion.
Reduce the heat to medium and add the grated kidneys. Cook for 5 minutes, stirring constantly.
Add the wine and cook for 5 minutes, stirring constantly.
Finally, add the tomato paste, tomato juice, salt and pepper. Cook for 30 minutes, stirring often.
When serving, spread the rice on plates, make a shallow hole in the middle and add boiling kidney sauce. Serve immediately.
NOTES:
Leftover sauce can be stored in the fridge for about a week. Bring the remaining sauce portions to a boil and serve over the rice as directed in the last step above.